1. Field of the Invention
The present invention relates to a method of measuring contamination and irradiation as well as a sensor for implementing this method.
It relates more particularly, but not exclusively, to the construction of a universal sensor of said type able to be constructed in a sufficiently miniaturized form so as to allow individual detection, for example for use by persons working in a radioactive environment who consequently run the risks of direct or indirect radiation by ionizing radiation, and/or contamination by radioactive substances in suspension.
2. Description of the Prior Art
At the present time there exists no portable individual sensor which may at the same time make irradiation or atmospheric contamination measurements in real time.
In fact, although measurement of irradiation may be made using individual portable apparatus such for example as pendosimeters, measurement of atmospheric contamination on the other hand requires relatively complex and expensive installations including necessarily:
devices for taking air from the monitored premises having aerolic connections, which, because of a depression engendered by a turbine, conduct the air flows taken to a filter for retaining the matter in suspension; PA1 a detector disposed in the immediate vicinity of the filter and adapted for measuring the activity of the radioactive materials retained by the filter; PA1 a device for processing the signals delivered particularly for obtaining a magnitude representative of the activity per unit of volume of the premisis; PA1 means for isolating the detection assembly (filter/detector) from the radioactivity coming from outside, these means being usually in the form of relatively heavy and bulky lead enclosures, guard counters, etc. . . . ; and PA1 a device for periodically changing the filters.
It has proved in practice that these installations have a number of drawbacks.
First of all, the measurement made by these installations is not truly representative of the harmful effects at the individual level, particularly because the atmosphere which reigns in the premises is usually not homogeneous and since the individual may move whereas the sampling point remains fixed. This problem is considerably aggravated when the premises are equipped with a system of ventilation.
Another drawback of these installations consists in the fact that they necessarily require a device for dynamically entraining the air with a complex regulation system so as to obtain a constant flow rate. Because the entrained air flow must pass through the filter, it is then advisable to use a pump or a turbine which is relatively powerful and consequently expensive and space consuming.
To this drawback is added the fact that the filter clogs progressively while inducing a variable pressure loss which the regulation system will have to counterbalance so as to maintain a constant flow and avoid degradation of the measurement.
Furthermore, the installations at present used are subject to the problem of contamination of the detector, due to the presence of this latter facing the filter. At the present time, this problem can only be resolved by regularily changing the detector, since the decontamination of this latter is a delicate operation.
In conclusion, these installations are costly to purchase and to run, they are heavy and therefore not easy to handle and cannot be readily increased in number. Furthermore, they are not strictly reliable for protecting persons for the above mentioned reasons. In addition, they are relatively complex since they require a different detection chain for each type of radiation and, in particular for detection of the contamination .alpha., the contamination .beta., for neutron irradiation, .gamma. irradiation and for the detection of radioactive gases such as krypton or xenon.
The purpose of the invention is then to overcome all these drawbacks. For this it provides a method implemented by means of a relatively simple, inexpensive universal sensor which may be used individually and which is capable of simultaneously effecting the different types of detection mentioned above.